similar: remove caching from the module level

similar: remove caching from the module level

To prevent Bad Things™ from happening, let's rework the logic to not use
util.cachefunc.

--- a/mercurial/similar.py	Mon Jan 09 11:01:45 2017 -0800
+++ b/mercurial/similar.py	Fri Jan 13 11:42:36 2017 -0800
@@ -13,7 +13,6 @@
 from . import (
     bdiff,
     mdiff,
-    util,
 )
 
 def _findexactmatches(repo, added, removed):
@@ -43,16 +42,14 @@
     # Done
     repo.ui.progress(_('searching for exact renames'), None)
 
[e-mail]
 def _ctxdata(fctx):
     # lazily load text
     orig = fctx.data()
     return orig, mdiff.splitnewlines(orig)
 
[e-mail]
-def score(fctx1, fctx2):
-    text = fctx1.data()
-    orig, lines = _ctxdata(fctx2)
+def _score(fctx, otherdata):
+    orig, lines = otherdata
+    text = fctx.data()
     # bdiff.blocks() returns blocks of matching lines
     # count the number of bytes in each
     equal = 0
@@ -64,6 +61,9 @@
     lengths = len(text) + len(orig)
     return equal * 2.0 / lengths
 
+def score(fctx1, fctx2):
+    return _score(fctx1, _ctxdata(fctx2))
+
 def _findsimilarmatches(repo, added, removed, threshold):
     '''find potentially renamed files based on similar file content
 
@@ -75,9 +75,12 @@
         repo.ui.progress(_('searching for similar files'), i,
                          total=len(removed), unit=_('files'))
 
+        data = None
         for a in added:
             bestscore = copies.get(a, (None, threshold))[1]
-            myscore = score(a, r)
+            if data is None:
+                data = _ctxdata(r)
+            myscore = _score(a, data)
             if myscore >= bestscore:
                 copies[a] = (r, myscore)
     repo.ui.progress(_('searching'), None)